To comply with the legal limits on emissions from internal combustion engines, different exhaust gas cleaning components as well as sensor units for regulating the internal combustion engine and monitoring emissions are used. For example, oxidation catalytic converters, diesel particle filters (DPF), SCR catalytic converters and NOx catalytic converters are known as exhaust gas cleaning components. Corresponding sensor systems include lambda sensors, NOx sensors and particle sensors.
Due to legal requirements which are being planned or have already gone into force, for example, the particle emissions of a motor vehicle which has an internal combustion engine designed, in particular, as a diesel engine, must be monitored upstream and/or downstream from a particulate filter during vehicle operation. According to the legislation, the monitoring of these components and sensor units for malfunctions and improper removal must furthermore be ensured. Such monitoring may be reliably ensured with the aid of a so-called on-board diagnosis (OBD).
For example, a method for monitoring a component situated in an exhaust gas area of an internal combustion engine is described in German Patent Application No. DE 103 58 195 A1, in which a measure for a first exhaust gas temperature is ascertained upstream from the component, and in which a second exhaust gas temperature, which occurs downstream from the component, is measured by a second temperature sensor. It is provided that the lowpass behavior, which is determined by the thermal capacity of the component, is checked by evaluating the first exhaust gas temperature in relation to the second exhaust gas temperature, and an error signal is output if a predefined measure for the lowpass behavior of the component changes.
This method may be used to assess the status of the component which is located between the two temperature sensors in the direction of the exhaust gas flow. For example, impermissible manipulations of this component as well as the complete removal of the component may thus be detected.
A collecting particle sensor is described in German Patent Application No. DE 101 33 384 A1 as an example of an exhaust gas sensor. The particle sensor is constructed from two meshing, comb-like electrodes which are at least partially covered by a collecting sleeve. When particles from the exhaust gas of the internal combustion engine accumulate on the particle sensor, this results in an analyzable change in the impedance of the particle sensor, from which the quantity of accumulated particles, and thus the quantity of particles carried in the exhaust gas, may be inferred. The particles accumulated on the particle sensor must be periodically burned off to make the sensor ready for measuring again. For this purpose, the particle sensor is heated to a predefined burn-off temperature, at which the particles oxidize, with the aid of a sensor heater.